A gas turbine is a turbo machine which generally comprises a compressor, a turbine and a combustor section. Ambient air which has been sucked in is compressed in the compressor and the compressed air is ultimately supplied to the combustor section. Arranged in the combustor section is at least one combustion chamber, mostly having a plurality of burners to which the compressed air is supplied. In addition to the compressed air, a fuel is also supplied to the burners which mixes with the air and is combusted. The resulting hot combustion gases are supplied to the turbine where they expand and cool down, thereby allowing the turbine to rotate. In so doing, the thermal energy from the combustion gases is converted into mechanical activity which on the one hand is used to drive the compressor and on the other hand is used to drive a load, for example of a generator for generating electricity.
It must be ensured that a stable flame is present during combustion in the combustion chamber. Flame instabilities occur in particular due to resonant combustion oscillations in the combustion gas and can lead on the one hand to increased pollutant emissions and on the other hand to oscillations and vibrations of the combustion chamber, which adversely affect the service life of the combustion chamber and shortens intervals between maintenance.
The combustion stability of gas turbines and other combustion plants is usually assessed using measurement signals, the timing of which fluctuates highly. These can be for instance measurement signals resulting from acceleration or pressure amplitude measurement on the combustion chamber. In order to suppress unwanted high-frequency components, the measurement signals are usually attenuated. However, peaks frequently occur at specific intervals over the height course of the measurement. This can also be referred to as a “picket fence” course. Between the peaks, the height drops to a completely non-critical value. A single peak also remains non-critical. Should the peaks repeat however, and if either the height of the peaks increases or the succession of peaks becomes more frequent, this indicates an incipient instability.
Up to now, what are known as peak hold value signals, also known as peak hold signals, have mostly been used for regulation. Here, only the maximum occurring height is relayed as a signal value for a defined time period. However, this signal does not provide any information about the frequency of the peaks. If the time window is large, a critical, high amplitude value is transmitted to the regulator, although under certain circumstances, only an individual, non-hazardous peak was present. If the time window is very small, so that per time period one peak is expected at the most, high and low signals alternate in rapid succession, resulting in an unsettled and often very inefficient regulation.